The present invention relates to a self-centering "joystick" input device capable of supporting multiple compound torque profiles for returning the joystick to the center position. Joystick input devices are well known in the art, and have been employed in a wide range of applications, from aircraft control to video game inputs. Joysticks may be provided to supply directional input information related to a single rotational axis, or to multiple axes. More sophisticated joystick instruments may provide magnitude data as well.
In operation, an operator will manually displace the joystick relative to one or more of its rotational axes in order to issue directional commands to other equipment. Sensors within the joystick will sense the angular displacement of the joystick and develop input signals accordingly, which may be transmitted to the equipment to be controlled. The sensors and the signals they produce may operate electronically, hydraulically, or otherwise.
In many applications it is desirable that the joystick return to a center or neutral position after it has been released by the operator. Many joysticks are designed to be displaced about two perpendicular axes, so that directional information may be detected through 360.degree.. Thus, in order to return the joystick to a center position on both axes, many designs have required two or more springs to provide a centering force relative to each axis. Some designs, for example that disclosed in U.S. Pat. No. 4,124,787 require two springs per axis. A problem with multiple spring designs is their complexity and higher cost. Also, most multiple spring designs include a significant amount of backlash around the center position. Backlash around the center position allows the joystick to be displaced by a small amount without developing an adequate restoring force to return the joystick to center. Thus, prior art instruments often include a slight wobble around the center position that can lead to inaccurate input measurements. The backlash problem is especially troublesome in applications where a high degree of accuracy and sensitivity is required.
A number of single spring designs have been developed in order to simplify the design of self-centering joysticks and reduce backlash. U.S. Pat. Nos. 4,479,038 and 5,724,068, for example, each employ a single spring to bias a thrust plate, or force plate, against a restoring member which is attached to the joystick itself. These designs prove simpler, and improve backlash around the center position, however, they are limited to providing a uniform restoring torque that is substantially equal in all directions.
In some applications it is desirable that the restoring torque for returning the joystick to the center position be greater in some directions than it is in others. Further, it may also be desired that the torque profile have a step such that the restoring torque is significantly increased if the joystick is displaced beyond a certain amount. Prior art joystick designs include no provisions for such multiple compound force profiles.